Capacitors for Microwave Applications

The properties and design of a metal-oxide-metal (MOM) capacitor are reviewed and its performance is compared with that of conventional MOS and metalized ceramic capacitors. The MOM structure is fabricated by growing a high-performance dielectric such as SiO2or Si3N4on silicon and metalizing the dielectric with several mils of copper, after which the silicon "handle" is removed and replaced with copper. The MOM capacitor has the high capacitance density, low dielectric loss, and low temperature coefficient properties of thermally grown dielectrics. In addition, the resistive electrode loss is minimized by the replacement of the Iossy silicon with copper. The electrode loss for the MOS and MOM capacitors is evaluated as a function of frequency and is in good agreement with the loss estimated from the surface sheet resistance. The series resistance of an MOM capacitor is only 10 percent of that measured for a comparable MOS structure. MOM capacitors have been successfully soldered into circuits; these assemblies have been temperature cycled and high temperature stressed.